Respiratory systems provide breathable gas, such as oxygen, anesthetic gas and/or air directly to a patient's mouth, nose or airway to assist or facilitate breathing by the patient. A ventilator may be used as part of the respiratory system to drive the breathable gas to the patient through an inspiratory limb hose or conduit of a breathing circuit. The breathing circuit may also include an expiratory limb hose or conduit to carry expelled air and other gas(es) from the patient back to the ventilator.
It is typically desired to warm and impart humidity to the breathable gas before it is provided to the patient. For that purpose, many respiratory systems include a humidification system having a heater unit and a disposable water chamber adapted to be heated by the heater unit. The heater unit supports a heater, such as a hot plate heater which may be comprised of one or more heating elements and a metal plate defining a hot plate. A wall of the chamber, such as the bottom surface thereof, is thermally conductive. The chamber is removably supported on the heater unit with the bottom surface in thermal contact with the hot plate of the heater unit to thus heat the water in the chamber. The breathable gas is coupled to the chamber and is passed through the chamber to be heated and humidified. Examples of heater units, chambers and vented water supplies are shown in U.S. Pat. Nos. 6,988,497 and 5,943,473; and co-pending U.S. patent application Ser. Nos. 11/469,086 and 11/469,113, both filed Aug. 31, 2006.
The inspiratory limb carries the heated and humidified gas to the patient and the expiratory limb, if present, carries exhaled air and possibly other gases from the patient. The hoses or conduits of the inspiratory and expiratory limbs may each be provided with a heater, referred to as a heater circuit, to add heat to the gas passing through the limb and to avoid the incidence of potentially dangerous or hazardous rainout of condensation from the gas(es) passing through the limb. The heater circuit may be in the form of one or more elongated, and possibly coiled, heater wires running along the limb, such as through the interior of the limb. An example of a breathing circuit with heated limbs is shown in U.S. Pat. No. 6,078,730.
The heater unit typically houses the necessary electrical and electronic components to regulate the temperature of the hot plate, as well as heating circuits, if present, of the inspiratory and/or expiratory limbs of the breathing circuit. Power to the heater unit can be disrupted in many ways, including due to problems with the electrical supply lines which is typically an AC supply, power outages or brownouts, AC voltage level drop-outs, or disconnection such as if the power cord used to plug the heater unit into the wall comes away from the heater unit or the wall plug. In some situations, power disruptions may go unnoticed yet can have serious adverse consequences to the patient. Moreover, with some of the complex electronics involved in some heater units, even otherwise minor power disruptions may lead to serious consequences if they are left unattended.